A nanofluid minimum quantity lubrication with addition of one kind of nanoparticle has several limitations, such as grinding of difficult-to-cutting materials Hybrid nanoparticles integrate the properties of two or more kinds of nanoparticles, thus having better lubrication and heat transfer performances than single nanoparticle additives However, the use of hybrid nanoparticles in nanofluid minimum quantity lubrication grinding has not been reported This study aims to determine whether hybrid nanoparticles have better lubrication performance than pure nanoparticle A hybrid nanofluid consisting of MoS2 nanoparticles with good lubrication effect and CNTs with high heat conductivity coefficient is investigated The effects of the hybrid nanofluid on grinding force, coefficient of friction, and workpiece surface quality for Ni-based alloy grinding are analyzed Results show that the MoS2/CNT hybrid nanoparticles achieve better lubrication effect than single nanoparticles The optimal MoS2/CNT mixing ratio and nanofluid concentration are 2:1 and 6 wt%, respectively

Experimental Evaluation of the Lubrication Performance of MoS2/CNT Nanofluid for Minimal Quantity Lubrication in Ni-based Alloy Grinding

This study investigates the critical maximum undeformed equivalent chip thickness for ductile-brittle transition (DBhmax-e) of zirconia ceramics under different lubrication conditions. A DBhmax-e model is developed through geometry and kinematics analyses of ductile-mode grinding. Result shows that DBhmax-e decreases with increasing friction coefficient (μ). An experimental investigation is then conducted to validate the model and determine the effect of dry lubrication, minimum quantity lubrication (MQL), and nanoparticle jet minimum quantity lubrication (NJMQL) conditions on DBhmax-e. According to different formation mechanisms of debris, the grinding behavior of zirconia ceramics is categorized into elastic sliding friction, plastic removal, powder removal, and brittle removal. Grinding forces per unit undeformed chip thickness (Fn/h and Ft/h) are obtained. The lubrication condition affects the normal force and ultimately influences the resultant force on workpiece. In comparison with dry grinding (DBhmax-e = 0.8 μm), MQL and NJMQL grinding processes increase DBhmax-e by 0.99 and 1.79 μm respectively; this finding is similar to model result. The theoretical model is then assessed by different volume fractions of nanofluids under NJMQL condition with an average percentage error of less than 8.6%.

Maximum undeformed equivalent chip thickness for ductile-brittle transition of zirconia ceramics under different lubrication conditions

Experimental evaluation of MoS2 nanoparticles in jet MQL grinding with different types of vegetable oil as base oil

Experimental evaluation of the lubrication performance of mixtures of castor oil with other vegetable oils in MQL grinding of nickel-based alloy

Experimental evaluation of the lubrication properties of the wheel/workpiece interface in minimum quantity lubrication (MQL) grinding using different types of vegetable oils

A heat transfer model for the precision grinding process on nano-zirconia ceramics has been investigated. Based on the analysis of the processing properties of nano-zirconia ceramic materials, a theoretical model for the temperature field in the grinding of nano-zirconia ceramics was established. The model was then simulated and analysed under different grinding conditions. The effect of temperature dependent thermal properties and heat flux profile on temperature distribution in the workpiece has also been investigated. Parametric studies were carried out to study the effect of different input parameters such as the depth of cut, work feed rate and grinding speed on temperature distribution in the contact zone and in the workpiece across the grinding width and along the direction of movement. The results showed that, as the grinding wheel cut into the workpiece, the workpiece temperature rose sharply, and then levelled-off, with a high temperature gradient on the surface of workpiece. As the grinding depth of cut increased, a local high temperature took place in the grinding contact zone.

Investigation into temperature field of nano-zirconia ceramics precision grinding

This paper describes an investigation about the grinding fluid optimization supply based on lubrication theory. The models for three-dimensional hydrodynamic flow pressure in contact zone between wheel and work are presented based on Navier-Stokes equation and continuous formulae. It is well known that hydrodynamic fluid pressure generates due to this fluid flux, and that it affects overall grinding resistance and machining accuracy. Moreover, conventional methods of delivering grinding fluid, i.e. flood delivery via a shoe or jet delivery tangential to the wheel via a nozzle, have been proved that they can not fully penetrate this boundary layer and thus, the majority of the cutting fluid is deflected away from the grinding zone. Therefore, in this paper, a new delivery method of grinding fluid, the minimum quantity lubricant (MQL)-near-dry green grinding is presented and analyzed for it not only reduces hydrodynamic lift force but also reduces grinding fluid cost to achieve green manufacturing. Experiments have been carried out to validate the performance of the MQL supply compared with conventional flood cooling. The experimental results have shown that the theoretical model is in agreement with experimental results and the model can well forecast hydrodynamic pressure distribution at contact zone between and workpiece and the MQL supply in grinding is feasible. Experiments have also been carried out to evaluate the performance of the MQL technology compared with conventional flood cooling. Experimental data indicate that the proposed method does not negatively affect to the surface integrity and the process validity has been verified.

Application of Lubrication Theory to Near-Dry Green Grinding – Feasibility Analysis

The models for three-dimensional velocity and hydrodynamic pressure of abrasive fluid in contact zone between wheel and workpiece on abrasive jet finishing with wheel as restraint were presented based on Navier-Stokes equation and continuous formulae. The emulational results shown that the hydrodynamic pressure was proportion to grinding wheel velocity, and inverse proportion to the minimum gap between wheel and workpiece and the maximum pressure was generated just in the minimum clearance region in which higher fluid pressure gradient occur. It can also be concluded the pressure distribution was uniform in the direction of width of wheel except at the edge of wheel because of the side-leakage. The velocity in the x direction was dominant and the side-leakage in the y direction existed. The velocity in the z direction was smaller than the others because of the assumption of laminar flow. The smaller the gap distance is, the larger the velocity in the x direction. The magnitude of the velocity is also proportional to the surface velocity of the wheel.

Model and Simulation of Slurry Velocity and Hydrodynamic Pressure in Abrasive Jet Finishing with Grinding Wheel as Restraint

The conventional method of delivering grinding fluid with a high supply of pressure and hydrodynamic fluid pressure can be generated ahead of the contact zone due to the wedge effect. In the present paper, theoretical hydrodynamic pressure modelling was applied to induce a flow of coolant fluid through the grinding zone during flood delivery grinding. The simulation results show that hydrodynamic pressure was proportional to grinding wheel velocity, and inversely proportional to the minimum gap between the wheel and workpiece surface. The maximum pressure value was generated in the minimum gap region where higher fluid pressure gradient occurred. Moreover, the hydrodynamic pressure at the wedge-shaped zone was also measured through experiments. The results suggest that the proposed model agrees with the theoretical model and it can accurately forecast changes in the hydrodynamic pressure at the contact zone between the grinding wheel and the workpiece.

Analytical and experimental investigation of grinding fluid hydrodynamic pressure at wedge-shaped zone

Structural parameters are important factors that affect the dynamic performance of the electrical spindle of high-speed grinder. In this study, the influences of the electric spindle's major structural parameters on its dynamic characteristics are investigated. Based on the transfer-matrix method and taking into consideration the gyroscopic couple, the shear, the variable cross-section, and other influential factors, a dynamic model is established for the multidisk rotor of the rotor-bearing system of the electric spindle. The critical speeds of first three orders, the modes of variation, and other dynamic characteristic parameters of the electric spindle are programmed and calculated. The influences of the axial pre-tightening force of the bearing, the span of the fulcrum bearing as well as the changes in the front and rear overhangs on the critical speed of the rotor-bearing system on the electric spindle and their pattern of changes are analyzed. The results show that the span of the fulcrum bearing and the overhang have significant influences on the critical speed within a certain range, and the study provide the basis and guidance for the structural design and performance optimization of the electric spindle.

Ya Li Hou

Papers

Investigation into temperature field of nano-zirconia ceramics precision grinding

Application of Lubrication Theory to Near-Dry Green Grinding – Feasibility Analysis

Model and Simulation of Slurry Velocity and Hydrodynamic Pressure in Abrasive Jet Finishing with Grinding Wheel as Restraint

Analytical and experimental investigation of grinding fluid hydrodynamic pressure at wedge-shaped zone

An analysis of the electric spindle's dynamic characteristics of high-speed grinder